In this study, pairs of the organosilicon/silicon oxynitride (SiO x N y ) barrier structures with an ultralow water vapor transmittance rate (WVTR) were consecutively prepared by the plasma-enhanced chemical vapor deposition at a low temperature of 70 • C using the tetramethylsilane (TMS) monomer and the TMS-oxygen-ammonia gas mixture, respectively. The thickness of the SiO x N y film in the barrier structure was firstly designed by optimizing its effective permeability. The WVTR was further decreased by inserting an adequate thickness of the organosilicon layer as the stress residing in the barrier structure was released accordingly. By prolonging the diffusion pathway for water vapor permeation, three-paired organosilicon/SiO x N y multilayered barrier structure with a WVTR of about 10 −5 g/m 2 /day was achievable for meeting the requirement of the thin film encapsulation on the organic light emitting diode.